I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
No padding is needed to plant in a half whiskey barrel. Make sure and drill a few 1/2 inch holes in the bottom for drainage. Then fill it with potting mix and plant. It should take a little over 4 cubic feet of potting mix to fill a half whiskey barrel.
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